Reply To: High(er) Voltage

[Stephen]

Thanks Andy. I know – I went a little too far down the rabbit hole. I was really befuddled. To complicate matters, the amp went silent after inserting a Weber MiniMass into the signal chain, before my teardown and testing. So I was scared that I did irreparable damage to something.

But I’m happy to report that I got it all reassembled, after making a few changes. I added the “pop-suppression” mod to the boost/voice switch. I redid all of the heater filament lines using a tighter twist with the “cordless drill” trick. Finally, I swapped out the 330V primary with the 300V primary on the PT. I redid a few solder points to tidy them up after soldering/desoldering/resoldering. And I replaced my homemade speaker wires with prefab ones. Plugging it in yesterday resulted in sound once again. YAY!

So I made a second attempt with the MiniMass, making sure it was all plugged in correctly. Played for a few minutes in Bypass mode at a low volume, then switched to Attenuate. This time, it worked. So I continued to play, gradually decreasing the volume on the MiniMass and increasing it on the Two-Stroke. I was FINALLY able to get some breakup, and could definitely notice the sag. With the Two-stroke wide-open and the MiniMass down almost all the way, it was really overdriving, getting a great roar from the 6V6. The pop-suppression worked as designed too. I used nothing other than my guitar, Two-stroke, and the MiniMass – no stompboxes. I’ll play around with the output tubes a bit (I have another 6V6 sitting here, plus an EL34 and a 6K6GT) and switch to the NOS RCA 5Y3GT rectifier too just for comparison. But I’m stoked to finally get the full potential out of it as far as output tube distortion and rectifier sag are concerned. I can always put my Rangemaster clone or another stomp in front if I want more preamp sizzle.

I took meter readings today, and between me switching the PT secondary and “whatever else” may have changed in my reassembly, the voltages are now under control. For posterity, here they are:

This is with the 125V primary and 300V secondary:

340-355 VDC at pin 3 of output tube
308-315 VDC at pin 4 of output tube
138-140 VDC at pin 1 of preamp tube
138-140 VDC at pin 6 of preamp tube
358 VDC at pin 8 of rectifier tube
313 VAC at pin 6 of rectifier tube
312 VAC at pin 4 of rectifier tube

Obviously, it’s now more “in-spec”, which makes me feel a lot better. I didn’t even have to get too creative with the voltage solutions; I just switched the secondary. The rectifier reflecting a proper voltage drop is especially relieving. With 313VAC going in and 358VDC coming out, it’s much closer to the expected voltage increase (1.1) for a 5Y3 at 1.14 times the VAC.

Perhaps Andy said it best by indicating this is a very forgiving amp. I doubt a SS amp and/or one with PCB’s would have survived the desoldering/resoldering, much less having voltages that were in considerable excess of the specs.

Keep on tubing!